Learning a Bias Correction for Lidar-only Motion Estimation

This paper presents a novel technique to correct for bias in a classical estimator using a learning approach. We apply a learned bias correction to a lidar-only motion estimation pipeline. Our technique trains a Gaussian process (GP) regression model using data with ground truth. The inputs to the model are high-level features derived from the geometry of the point-clouds, and the outputs are the predicted biases between poses computed by the estimator and the ground truth. The predicted biases are applied as a correction to the poses computed by the estimator. Our technique is evaluated on over 50km of lidar data, which includes the KITTI odometry benchmark and lidar datasets collected around the University of Toronto campus. After applying the learned bias correction, we obtained significant improvements to lidar odometry in all datasets tested. We achieved around 10% reduction in errors on all datasets from an already accurate lidar odometry algorithm, at the expense of only less than 1% increase in computational cost at run-time.Comment: 15th Conference on Computer and Robot Vision (CRV 2018

The lambda-dimension of commutative arithmetic rings

It is shown that every commutative arithmetic ring $R$ has $lambda$-dimension $leq 3$. An example of a commutative Kaplansky ring with $lambda$-dimension 3 is given. If $R$ satisfies an additional condition then $lambda$-dim($R$

Chemical Evolution of the Juvenile Universe

Only massive stars contribute to the chemical evolution of the juvenile universe corresponding to [Fe/H]<-1.5. If Type II supernovae (SNe II) are the only relevant sources, then the abundances in the interstellar medium of the juvenile epoch are simply the sum of different SN II contributions. Both low-mass (~8-11M_sun) and normal (~12-25M_sun) SNe II produce neutron stars, which have intense neutrino-driven winds in their nascent stages. These winds produce elements such as Sr, Y, and Zr through charged-particle reactions (CPR). Such elements are often called the light r-process elements, but are considered here as products of CPR and not the r-process. The observed absence of production of the low-A elements (Na through Zn including Fe) when the true r-process elements (Ba and above) are produced requires that only low-mass SNe II be the site if the r-process occurs in SNe II. Normal SNe II produce the CPR elements in addition to the low-A elements. This results in a two-component model that is quantitatively successful in explaining the abundances of all elements relative to hydrogen for -3<[Fe/H]<-1.5. This model explicitly predicts that [Sr/Fe]>-0.32. Recent observations show that there are stars with [Sr/Fe]<-2 and [Fe/H]<-3. This proves that the two-component model is not correct and that a third component is necessary to explain the observations. This leads to a simple three-component model including low-mass and normal SNe II and hypernovae (HNe), which gives a good description of essentially all the data for stars with [Fe/H]<-1.5. We conclude that HNe are more important than normal SNe II in the chemical evolution of the low-A elements, in sharp distinction to earlier models. (Abridged)Comment: 10 pages, 9 figures, to appear in Pub. Astron. Soc. Australi

Structural trends and basement rock subdivisions in the western Gulf of St. Lawrence, northern Appalachians

We compiled industry seismic and LTTHOPROBE deep seismic data in the southwestern Gulf of St. Lawrence, and interpreted them together with gravity, magnetic and industry well data, to study the deepest sediments, which are assignable to the Horton Group of Late Devonian-Early Carboniferous age, and the basement rocks of the northern Appalachians. Three upper crustal basement blocks with differing seismic character and orientation of geological structures were identified. South of the Appalachian structural front and parallel to it, two blocks with a northwest regional strike were interpreted to be allochthonous on Grenvillian crust. The basement block immediately south of the Appalachian structural front (Laurent) shows deformations compatible with Acadian or older northward thrusting, whereas the second (Bradelle) displays north dipping reflections, possibly related to formation of the Magdalen Basin. These basement blocks may contain the offshore extensions of either the Humber or Dunnage Appalachian terranes, or both. The Catamaran, Fredericton, and Belleisle faults in New Brunswick appear to extend to the northeast across the third basement block (Shediac), parallel to the main structural trends in this block. The Shediac block contains the extensions of the Gander and Avalon terranes, and the deep seismic data suggest that the Gander/Avalon boundary cuts through the entire crust This compilation enabled us to address the problem of the formation of the Magdalen Basin. Several Horton Group subbasins, bounded by normal faults, indicate a widespread crustal extension phase which coincided with the early development of the Magdalen Basin. Compressive strike-slip movement inferred from the seismic data along the Belleisle Fault suggested that this fault played a major role in the formation of the basin, but crustal stretching occurred in an area not bounded by this fault The overall asymmetry of the Magdalen Basin suggests that dip-slip movement occurred along a fault (the Hollow Fault?) bounding the basin to the east. The existence of a "Canso Fault" at the location proposed by several authors is not supported by our work. A better candidate for its location may be along the Bradelle/Shediac basement block boundary. R&#xC9;SUM&#xC9; Nous avons compil&#xE9; les donn&#xE9;es acquises &#xE0; l'aide de la sismique industrielle et de la sismique &#xE0; forte p&#xE9;n&#xE9;tration LTTHOPROBE en provenance du sud-ouest du Golfe du Saint-Laurent, les avons interpr&#xE9;t&#xE9; en conjonction avec les donn&#xE9;es gravitaires, magn&#xE9;tiques et de forage industriel, et ce dans le but d'&#xE9;tudier les s&#xE9;diments les plus profonds, attribuables au Groupe de Horton d'&#xE2;ge d&#xE9;vonien tardif &#xE0; carbonif&#xE8;re pr&#xE9;coce, ainsi que les roches constituant le socle dans les Appalaches septentrionales. On identifia trois blocs de socle supracrustaux montrant des configurations sismiques et une orientation des structures g&#xE9;ologiques diff&#xE9;rentes. On interpr&#xE8;te comme allochtones stir une cro&#xFB;te grenvillienne deux blocs ayant une direction r&#xE9;gionale nord-ouest, situes au sud du front structural appalachien et parall&#xE8;le les &#xE0; ce dernier. Le bloc de socle sis juste au sud du front structural appalachien (bloc de Laurent) montre des d&#xE9;formations compatibles avec un chevauchement vers le nord acadien ou plus ancien, alors que l’autre bloc (bloc de Bradelle) pr&#xE9;sente des r&#xE9;flexions pent&#xE9;es nord et reli&#xE9;es possiblement &#xE0; la formation du Bassin de la Madeleine. Ces blocs de socle pourraient contenir les extensions vers le large des lanieres appalachiennes de Humber et/ou de Dunnage. Les failles de Catamaran, de Fredericton et de Belleisle, au Nouveau-Brunswick, semblent se prolonger vers le nord-est par-dela le troisi&#xE8;me bloc de socle (bloc de Shediac); elles sont parall&#xE8;les aux principales tendances structurales &#xE0; l'int&#xE9;rieur de ce bloc. Le bloc de Shediac contient les prolongements des lani&#xE8;res de Gander et d'Avalon; les donn&#xE9;es de la sismique &#xE0; forte p&#xE9;n&#xE9;tration sugg&#xE8;rent que la frontiere Gander/Avalon traverse toute l'ecorce. Cette compilation nous &#xE0; permis d'envisager le probl&#xE8;me de la formation du Bassin de la Madeleine. Plusieurs petits sous-bassins, appartenant au Groupe de Horton et limites par des failles normales, indiquent une phase r&#xE9;pandue d'extension crustale qui coiincida avec l'amorce du Bassin de la Madeleine. Un d&#xE9;crochement en compression, inf&#xE9;r&#xE9; des donn&#xE9;es sismiques, le long de la Faille de Belleisle sugg&#xE8;re que cette faille joua un role majeur dans la formation du bassin bien que retirement crustal survint dans une r&#xE9;gion non limit&#xE9;e par cette faille. L'asymettie d'ensemble du Bassin de la Madeleine sugg&#xE8;re que le mouvement selon le rejet-pente se produisit le long d'une faille (Faille de Hollow?) limitant le bassin a Test. Nos travaux ne confortent pas l'hypoth&#xE8;se d'une "Faille de Canso" &#xE0; l'endroit avarice1 par phisieurs auteurs. Un meilleur site pour sa localisation serait le long de la fronti&#xE8;re entre les blocs de socle de Bradelle et de Shediac. [Traduit par le journal

Selfduality for coupled Potts models on the triangular lattice

We present selfdual manifolds for coupled Potts models on the triangular lattice. We exploit two different techniques: duality followed by decimation, and mapping to a related loop model. The latter technique is found to be superior, and it allows to include three-spin couplings. Starting from three coupled models, such couplings are necessary for generating selfdual solutions. A numerical study of the case of two coupled models leads to the identification of novel critical points

The 2-D electron gas at arbitrary spin polarizations and arbitrary coupling strengths: Exchange-correlation energies, distribution functions and spin-polarized phases

We use a recent approach [Phys. Rev. Letters, {\bf 84}, 959 (2000)] for including Coulomb interactions in quantum systems via a classical mapping of the pair-distribution functions (PDFs) for a study of the 2-D electron gas. As in the 3-D case, the ``quantum temperature'' T_q of a classical 2-D Coulomb fluid which has the same correlation energy as the quantum fluid is determined as a function of the density parameter r_s. Spin-dependent exchange-correlation energies are reported. Comparisons of the spin-dependent pair-distributions and other calculated properties with any available 2-D quantum Monte Carlo (QMC) results show excellent agreement, strongly favouring more recent QMC data. The interesting novel physics brought to light by this study are: (a) the independently determined quantum-temperatures for 3-D and 2-D are found to be approximately the same, (i.e, universal) function of the classical coupling constant Gamma. (b) the coupling constant Gamma increases rapidly with r_s in 2-D, making it comparatively more coupled than in 3-D; the stronger coupling in 2-D requires bridge corrections to the hyper- netted-chain method which is adequate in 3-D; (c) the Helmholtz free energy of spin-polarized and unpolarized phases have been calculated. The existence of a spin-polarized 2-D liquid near r_s = 30, is found to be a marginal possibility. These results pertain to clean uniform 2-D electron systems.Comment: This paper replaces the cond-mat/0109228 submision; the new version include s more accurate numerical evaluation of the Helmholtz energies of the para- and ferromagentic 2D fluides at finite temperatures. (Paper accepted for publication in Phys. Rev. Lett.

Étude exploratoire des caractéristiques professionnelles d&#039;un échantillon de suicidants hospitalisés

Cette étude a pour objectif de décrire les caractéristiques professionnelles d’un échantillon de suicidants. Un enquêteur a interrogé les suicidants âgés de 18 à 65 ans, hospitalisés consécutivement dans une unité spécialisée du CHU d’Angers sur une durée de 6 mois et demi. Au total, 87 suicidants actifs avec un emploi ont été interrogés. Ils ont souvent été confrontés à des contraintes organisationnelles décrites dans la littérature comme responsables de souffrance mentale liée au travail. Cela concerne globalement autant les hommes que les femmes. En comparaison aux enquêtes de santé au travail (Sumer, Samotrace…), les suicidants sont plus nombreux à ressentir entre autres un stress intense au travail, une conscience professionnelle heurtée et à être en situation tendue selon le modèle de Karasek. Cela pourrait être en faveur d’un lien entre les tentatives de suicide et certains facteurs de pénibilité mentale au travail. Les résultats de cette étude sont à interpréter avec prudence du fait des phénomènes de circularité des données et de la faiblesse de l’échantillon

Vlasov moment flows and geodesics on the Jacobi group

By using the moment algebra of the Vlasov kinetic equation, we characterize the integrable Bloch-Iserles system on symmetric matrices (arXiv:math-ph/0512093) as a geodesic flow on the Jacobi group. We analyze the corresponding Lie-Poisson structure by presenting a momentum map, which both untangles the bracket structure and produces particle-type solutions that are inherited from the Vlasov-like interpretation. Moreover, we show how the Vlasov moments associated to Bloch-Iserles dynamics correspond to particular subgroup inclusions into a group central extension (first discovered in arXiv:math/0410100), which in turn underlies Vlasov kinetic theory. In the most general case of Bloch-Iserles dynamics, a generalization of the Jacobi group also emerges naturally.Comment: 45 page

Negative differential resistance in nanotube devices

Carbon nanotube junctions are predicted to exhibit negative differential resistance, with very high peak-to-valley current ratios even at room temperature. We treat both nanotube p-n junctions and undoped metal-nanotube-metal junctions, calculating quantum transport through the self-consistent potential within a tight-binding approximation. The undoped junctions in particular may be suitable for device integration.Comment: 4 pages, 4 figures, to appear in Physical Review Letter